1. Field of the Invention
The present invention relates to an object position measuring system and device for use in measuring without contact, fine displacement amounts of an object, conditions of an object surface, and so on.
2. Description of the Prior Art
With the growth of factory automation in recent years, and more specially in the manufacturing processes of various products, there has been an increasing demand for measurement of displacement amounts and surface conditions of the products in order to control the positions of the products or to check surface finish conditions of the same. Especially, in the case of such products as lenses or mirrors which are vulnerable to clouds because of vapor film formed on surfaces thereof or as a semiconductor which is vulnerable even to small external forces, it is essential that the displacement amount or the surface condition measurement be carried out in a non-contact method.
Most of object displacement amount or surface condition measuring systems of the above non-contact type utilize a light beam. It is to be noted here that the measurement of object displacement amount or surface condition will be generically referred to as object position measurement in the following description of the present invention.
One of the most typical conventional position measuring systems carries out the object position measurement by the focusing of a microscope. This system utilizes in combination, a microscope and a focus detecting mechanism for use e.g. in the field of the digital audio disk. In operation, the object position measurement is carried out by detecting focusing or focusing error on an enlarged surface of an object to be inspected.
Another conventional position measuring system employs a light beam reflecting type sensor using an optical fiber cable. In operation, a light beam is applied onto an inspection object through an optical fiber having a predetermined projection angle at an end thereof and the beam reflected from the object enters the optical fiber having the predetermined light receiving angle. Then, the object displacement amount is obtained by measuring the amount of light received by the optical fiber.
That is to say, the beam projecting fiber and the beam receiving fiber have the predetermined projecting angle, and the predetermined receiving angle respectively. Thus, if these fibers are displaced with a predetermined distance, the amount of light received by the receiving fiber varies in accordance with a variation in the displacement amount of the object. Therefore, it is possible to obtain the displacement amount by calculating the variation in the amount of the received light.
However, with the above conventional systems, there are problems. These problems will be described next.
In the case of the former system utilizing focusing of a microscope, it is necessary to increase a magnification of an object lens in order to achieve a high precision measurement. However, with the increased magnification of the object lens, the distance between the object and the lens becomes very short. This means that the operative distance (range) of the measuring device, i.e. the distance which permits the measuring device or the object to move freely without coming into contact with the other, becomes short. Therefore, it is difficult to measure an object having surface unevenness.
The second system mentioned above measures variation in the amount of a light beam reflected from the object. It is easy to measure an object displacement amount with high sensitivity in a region adjacent the open end of the fiber since the variation in the received light fluctuates very conspicously about the peak of received light amount in this region. However, if the object is disposed distantly from the peak, the amount does not vary so conspicuously. For this reason, the operative range of the device need be sacrificed for the sake of high measuring precision, and it is difficult for this system to measure an object having a large displacement amount variation or having considerable surface unevenness.